Re: Help fixing AOC Plasma (Samsung board)

On Aug 12, 4:36 pm, Franc Zabkar <fzab...@xxxxxxxxxxxxxxxxx> wrote:
On Tue, 12 Aug 2008 11:37:37 -0700 (PDT), Chrisroberts7577
<chrisroberts7...@xxxxxxxxx> put finger to keyboard and composed:

I need help getting help, finding a replacement board, or even finding
the schematic for an AOC (A42HD84) Plasma tv.  I believe the main
power supply board (Samsung, LJ44-00092C) is the problem.

When I got the TV there was a blown fuse on the board.  See some pics
of the board here:http://chrisroberts7577.googlepages.com/plasmarepair

When the board gets power there is only one voltage correctly present,
all others are non-existent.

Any help or guidance anyone can provide would be greatly appreciated.

At the risk of stating the obvious, the fact that you are getting only
one voltage (the standby voltage?) suggests that your set is not
coming out of standby.

One thing that strikes me straight away is that the solder joints
around various coils (L465 & L466 & L341 ?) are not shiny. I usually
reflow the solder at all the coils, whether good or bad.

http://chrisroberts7577.googlepages.com/IMG_3017.jpg/IMG_3017-full;in...

The most obvious approach is to trace out the circuit around the blown
fuse, or at least test all the active components in that area. Likely
culprits would be the two MOSFETs on the adjacent heatsink which would
probably be driven by the IR2109 Half-Bridge Driver IC:

http://www.irf.com/product-info/datasheets/data/ir2109.pdf

Another candidate could be an open NTC resistor near the fuse. These
resistors are used to limit the inrush current to the main bulk
capacitor(s).

There must also be a signal (PS_ON ?) coming in via this board ...

http://chrisroberts7577.googlepages.com/IMG_3022.jpg/IMG_3022-full;in...

... that switches on the main PSU. Confirm that this signal is
changing state when you turn the set on, and then check to see that
the output of this board is switching the AC supply.

BTW, AOC is a well known monitor manufacturer.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Frank thanks for your help. Here are some answers to your questions.

The TV is going from standby to the ON state fine. I've checked that
small board and it seems to be doing it's job correctly. The LED on
the TV changes colors when I press the on button, you hear a relay
switch, and that's when the single voltage on the main board appears.
The TV will not switch back into the standby state however.

I will try reflowing those solder joints tomorrow if I can remember to
bring the board in to work. I was really disappointed in the quality
of the board when I took a look at it. There is still flux all over
it, like it never got cleaned.

I should be able to check the mosfet and resistor tonight. Hopefully
I can find something.

Thanks for your input.



.

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